Answers

Hmm… No offense, but I don't know why you doesn't use the honorific like '－요' or '-ㅂ니다', 果報者.

A noun ending with the final consonant + 이에요
점심 시간이에요. It's time to have lunch.
얘는 제 남동생이에요. This is my (younger)brother.
책이에요 It's a book.

A noun ending with a vowel or double one + 예요
저 지금 학교예요. I'm now at school.
이거 제 목도리예요. This is my muffler.

There are two exceptions to this. When you say one's name ending with the final consonant, you have to use 이예요.
제 이름은 지현이예요.
제 이름은 동건이예요.
When you combine one's name ending with the final consonant with the postposition, 이(an ending) is being added to the end the name.
지은 + 이 + 는 안 왔어요.
지은 + 이 + 를 여기로 보내세요.
지은 + 이 + 가 했어요.

So, 지현이 + 이에요 = 지현이예요, 동건이 + 이에요 = 동건이예요.

About 아니에요, it is formed by combining 아니-(the stem of the adjective) + -에요(an ending). So 아니예요 is grammartically wrong.

@Hailey
Interesting to see your explanation. Could you please recite your reference for this? My reference didn't explicitly point out the rules and the exceptions. So, it will be great to learn from another resource :)

＠Mike I've just checked your Korean level. Okay, you'll see some grammatical terms in this explanation. I'm gonna make it easy, I'm not sure if I can pull off though :b

First of all,「-이」is a descriptive postposition. It's combined with the ending like「-ㅂ니다」,「-에요」,「-죠(an abbreviation for '지요')」
I don't care. 전 신경 안 씁니다.
I'm Korean. 전 한국인이에요.
Who says that way is a moron. 그렇게 말하는 사람이 바보죠.

Second of all, as you saw all of the above,「이에요」is used after a noun ending with the final consonant, and「예요」is used after a noun ending with the vowel.
Let's take「제 동생이예요」to see how the rule works. You know it's wrong. In it,「에」is influenced by the vowel「이」(If you try to pronounce 제 동생이에요, you can find out.) This phenomenon is called "Progressive Assimilation Of Vowels". But the rules of Korean orthgraphy don't reflect it in written Korean, it's why「제 동생이예요」is wrong. Then someone could raise this kind of question, "Isn't reasonable to see this way「제 동생(ending with the final consonant) + 이(the postposition) + 예요」if 제 동생이 했어요 is correct?" Yeah, the matter is that 예요 doesn't exist in Korean as an ending.

About「동건이예요」, the last syllable of「동건」ends with the consonant, so「이」comes to the end of it.「동건」+「이」+「이에요」=동건이이에요. You see two 이s bump into each other in it, and it seem not to follow the economy principle of the language. So it becomes 동건이예요 by shortening「이에요」. As another example, 미희이에요 isn't wrong, just all people abbreviate「이에요」. Keep this in mind, that what comes before「이」is 동건이, not 동건.

As for「아니에요」,「아니」means 'denial' or 'disapprove' and is combined with 에요(a terminative ending). 아니예요 is wrong because 예요 doesn't exist as an ending in Korean.
Also 아니이에요 doesn't make sense because the meaning of「아니」and「이에요 am, are, is」 It's just like "No, it is" is wrong. The abbreviated one is 아녜요.